Separation of suspensions of solid matter in liquids



Oct. 6, 1953 DRIESSEN 2,654,479

SEPARATION OF SUSPENSIONS OF SOLID MATTER IN LIQUIDS Original Filed Aug. 8, 1959 THICKENED SUSPENSION DILUTED SUSPENSION CLARIFIED WATER MAXIMILIAAN 6. DRIESSEN DECEASED. BY ANTJEG. DRIESSEMADMINISTRATOR .v jua wawzww Patented Oct. 6, 1953 SEPARATION OF SUSPENSIONS OF SOLID MATTER IN LIQUIDS Maximiliaan G. Driessen, deceased, late of Pittsburgh, Pa., by Antje G. Driessen, administrator, Amsterdam, Netherlands, asslgnor to De Directie van de Staatsmijnen, Washington, D. 0., a corporation of the Netherlands Application August 9, 1951, Serial No. 241,069

In the Netherlands December 28, 1938 Claims. (Cl. 209173)' This application is a continuation of application Serial No. 288,954, filed August 8, 1939. In more detail, the present application is a di-v vision of application Serial No. 787,899, filed November 25, 1947, which was a continuation of application Serial No. 422,794, filed December 13, 1941, which was a continuation-in-part of said application Serial No, 288,954. I

This invention relates to the separation or concentration of suspensions in coal or ore preparation plants and more particularly of suspensions used in the separation of coal and rock by means of so-called heavy liquors.

These heavy liquors are for instance suspensions of loess, clay, fine slate, baryte, magnetite and the like.

In such processes the separated products, namely coal and rock, are rinsed with water, whereby diluted suspensions of the washing agents, viz. loess, clay, slate, baryte or magnetite are obtained. From these diluted suspensions the Washing agents must in most cases be recovered by-separaticn or thickening the suspension. Also when the heavy liquor is a true liquid, such as for instance carbon tetrachloride or a salt solution, such as for instance a calcium nitrate solution, it becomes necessary in the course of the treatment to regenerate the washing agent impurified with coal dust and rock dust. Consequently an important part of the necessary plant is always destined for the separation or concentration (thickening) of suspensions.

Besides apparatus for regenerating washing agents, also equipment is necessary for e. g. clarifying waste water if desired after addition thereto of flocculating agents. Thus also when applying for instance the ordinary washing method with liquid currents, jig, foam flotation, etc, apparatus are necessary for recovering coal fines from suspensions and apparatus for the separation of rock mud.

Up till now it was usual to separate all these suspensions by application of classifiers, thickeners, e. g. Dorr thickeners or V-shaped tanks Spitzkasten) serious drawback of a relatively very large size. Moreover, serious difficulties can arise by clogging, in those apparatus in which the thickened material is removed through an opening in the bottom.

To obtain an improved operation of the system stirrers are present in thickeners e. g. Dorr thickeners. When, however, the concentration of the too much in the course of the treatment, the stir- All these apparatus have the may break. It has been suggested to eliminate this drawback by means of a device which automatically lifts the stirrer if the stresses become too high so that the stirrer exerts its action in thinner layers. This device, however, was not always satisfactory. The lifted stirrer does not sufliciently fulfil its purpose and the mechanism is far more complicated.

According to the invention the suspensions formed in coal washing plants and particularly the suspensions occurring in the separation of coal and rock by means of heavy liquors are separated in simple and efilcient way by means of a cyclone into two fractions of controllable concentrations.

Up till now the use of cyclones for the separation of suspensions was only indicated in connection with the paper industry, French Patent No. 828,643, United States Patent to Freeman No. 2,102,525, issued December 14, 1937, and British Patent No. 455,845, and UnitedStates Patent to Berges, No. 2,098,608, issued November 9, 1937.

These patents disclose vortex separators having circular separating spaces into which liquid suspension is introduced tangentially to create vortices and in which there are axially spaced axial outlets. From these specifications nothing can be derived, however, with regard to the application of the cyclone in coal washing. Moreover the problem of the separation of suspensions in coal washing has a very particular aspect. In this case namely not only the obtaining of a suspension as highly concentrated as possible or the most complete clarification of waste water is aimed at but it is also of the highest importance to have a method available for thickening a suspension to a very definite concentration.

If it is desired for instance in coal washing by means of a loess suspension (specification No. 13,472/38) to recover the loess rinsed off from the spraying water flowing from the separated coal and rock, the most economical method is to recover the rinsed loess in the form of a concentrated suspension of the same density as the density of the washing medium. In such a method the recovered loess can immediately be added again into the coal washing tank. The density of the washing medium may be selected higher or lower, depending on the requirements demanded of the separation of coal and rock. Consequently the thickening process must be variable so that it may produce suspensions of different concentrations.

It has appeared that for thickening suspenpressure under sions to a very definite density a cyclone is excellently suitable. According to the invention the densitiesof both the fractions of the suspension separated in the cyclone may be easily controlled vnamely by suitable adoption of the diameter of the outlet opening for the heavier fraction and/or the diameter of the outlet opening for the lighter fraction. Moreover the densities may be controlled by suitably selecting the which the suspension is supplied.

By diminishing the diameter of the outlet opening of the heavier fraction and/or by increasing the diameter or the outlet opening of On account of the ease of control of the thickening process by the application of a cyclone the process has great advantages with regard to other concentration methods.

Still other advantages, however, are obtained by application of a cyclone. The construction issimple and cheap, the power consumption is low,

:the reliability is high, moving parts are not present, few workmen are required for supervision,

the control may be effected automatically. Furthermore there is an enormous saving in space by the application of the cyclone. In order to obtain the same output as e. g. a Dorr thickener the cyclone only requires $4 of the base area. The separation by means of a cyclone may be called dynamic in contradistinction to the previous static separation method by means of thickeners, etc. In consequence hereof clogging of outlet openings practically does not occur in cyclones. The solid material of the heavier fraction has no occasion to deposit.

The separation by means of a cyclone may also be combined with application of foamflotation methods in the cyclone, for ,instance with addition of oil and fine air bubbles. Hereby the flotating particles are quickly separated from the rest of the suspension.

Though the separation of solid constituents from suspensions such as occur in coal washing plants by means of a cyclone is usually not quantitively complete it has appeared to be satisfactory in practice.

' consists in the preparation of suspensions to be used as heavy liquor, of some materials which otherwise would be unsuitable to this purpose for instance certain earths consisting of a mixture of sand and clay. From such material a diluted suspension is prepared which is then subjected to separation in a cyclone. The lighter fraction removes the unsuitable constituents from the suspension; the heavier fraction may be used as heavy liquid for the separation of coal and rock.

The invention is illustrated by the following example.

This example describes in connection with a washing plant using as heavy liquor a .15-

into the heavier fraction, de-

pension of a specific gravity of 1.5, a thickening of the rinsing water obtained by rinsing the separated coal and rock, which rinsing water is-thicksued to a suspension which maybe directly added to the separation medium.

The capacity of the washing plant is 100 tons of coal per hour.

The quantity of rinsing water flowing from the lsleparated' coal and rock amounts to in. per

our. I

To this end two parallel cyclones are necessary with a diameter of the bottom area of 50 cm. In order to thicken the suspension to a specific gravity of 1.5 the cyclones must be controlled in suitable manner, for instance a specific gravity of 1.5 may be obtained by using the following conditions:

Diameter outlet opening lighter fraction m 45 Diameter outlet opening heavier fraction 'mm 10 Pressure under which the suspension is supplied atmospheres 2 If the lighter fraction is still passed through a second set of cyclones having a diameter of 50 cm. the total recovering figure is about 80%.

The accompanying diagrammatic drawing suspension flowing from the sieves 3 and 5 is led over a vibrating sieve 8, which removes coarser particles from the suspension to the collecting tank I and is then pumped by pump 8 to the cyclones 9 of which the figure only shows one. In these cyclones the diluted suspension is exposed to centrifugal action on account of which, there is formed on one hand a thickened suspension and on the other hand clarified water. The thickened suspension goes from these cyclones 9 to the store tank It! and finally to the washing tank I. The water clarified by the cyclones 9 streams to the store tank H from which it passes as rinsing water to the sieves 8 and 5 or it may be passed over an overflow to the cyclones II. In the cyclones I l the water is further freed from solid particles and then removed at c. The heavier fraction from the cyclones ll flows into the collecting tank I. As is apparent from the above description the withdrawal of suspension from the apex of the cone 9 is in a continuous stream.

At a fresh suspension is supplied, at b clean water may be introduced, at c clarified water is removed.

What is claimed is:

1. In a coal cleaning process employing aheavy medium comprising a stable suspension of finely divided solids in water, the steps for regenerating the medium from medium solids rinsed from the coaland residue as a dilute slurry, comprising feeding the dilute slurry of said medium solids under a feed pressure of the order of two atmospheres tangentially into one end of a circular elongated separating space, removing axially as a stream of restricted diameter from the end adjacent the tangential feed a suspension of medium solids in water having a lower specific gravity than the slurry, continuously removing axially from the other end of the space as a stream of restricted diameter a concentrated suspension of medium solids in water having the constant specific gravity of the original heavy medium of the coal cleaning process, and regulating the feed pressure and the diameters of the two axial discharge streams in such manner as to maintain constant said specific gravity of the concentrated suspension and returning the concentrated suspension to the coal cleaning process.

2. In a mineral dressing process employing a heavy medium comprising a suspension of finely divided solids in water, the steps for regenerating the medium from medium solids rinsed from the mineral and residue as a dilute slurry, comprising feeding the dilute slurry of said medium solids under a feed pressure of the order of two atmospheres tangentially into one end of a circular elongated separating space, removing axially as a stream of restricted diameter from the end adjacent the tangential feed a suspension of medium solids in water having a lower specific gravity than the slurry, continuously removing axially from the other end of the space as a stream of restricted diameter a concentrated suspension of medium solids in water having the constant specific gravity of the original heavy medium of the mineral dressing process, and regulating the feed pressure and the diameters of the two axial discharge streams in such manner as to maintain constant said specific gravity of the concentrated suspension and returning the concentrated suspension to the mineral dressing process.

3. In a mineral dressing process employing a heavy medium comprising a suspension for finely divided solids in a liquid, the steps to producing a heavy medium having the specific gravity of the separation comprising feeding the dilute slurry of said medium solids under a feed pressure or the order of two atmospheres tangentially into one end of a circular elongated separating space, removing axially as a stream of restricted diameter from the end adjacent the tangential feed a suspension or medium solids in liquid having a lower specific gravity than the slurry, continuously removing axially from the other end of the space as a stream of restricted diameter a concentrated suspension or medium solids in liquid having the constant specific gravity or the original heavy medium of the mineral dressing process, and regulating the feed pressure and the diameters of the two axial discharge streams in such manner as to maintain constant said specific gravity of the concentrated suspension.

4. In a process employing a suspension or finely divided solids in a liquid, the steps for producing a suspension having a desired concentration comprising feeding the finely divided solids in said liquid as a dilute suspension under a feed pressure tangentially into one end or a circular elongated vortex space, removing axially as a stream or restricted diameter from the 'end adjacent the tangential feed a suspension or finely divided solids in liquid having a lower concentration than the'inieed suspension, continuously removing axially from the other end or the space as a stream or restricted diameter a concentrated suspension or finely dividedsolids in liquid having the desired concentration, and regulating the reed pressure and the diameters or the two axial ANTJE G. DRIESSEN. Administrator of the Estate of Maximz liaan G.

Driessen, deceased.

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